1. Field of the Invention
The invention generally relates to a coolant recovery and recycling apparatus. In one aspect, the invention relates to a helium recovery and recycling apparatus associated with a heat exchanger.
2. Description of the Related Art
In the production of optical fibers, a glass rod or a “pre-form”, which is especially made to manufacture optical fibers, is processed in an optical fiber drawing system. The optical fiber drawing system generally comprises a furnace, a heat exchanger, a coating applicator, a dryer or curing furnace, and a spool as illustrated in European Patent Application No. 0079188. Initially, the glass rod is melted in the furnace such that a small, semi-liquid fiber is produced. The semi-liquid fiber is then cooled and solidified while falling through the air and the heat exchanger. Thereafter, the cooled, solidified fiber can be coated in the coating applicator, dried in the curing furnace or dryer, and drawn with the spool.
The drawing rate of the optical fiber is generally dependent upon the cooling rate of the optical fiber in the heat exchanger. That is, the rate at which the fiber can be drawn increases as the rate at which the fiber can be cooled increases. To increase the cooling rate of the optical fiber, a direct heat exchange process is employed. In the direct heat exchange process, a coolant gas (e.g., helium, nitrogen, a helium-nitrogen mixture, a helium-air mixture, a helium-argon mixture, a helium-hydrogen mixture, a helium-inert gas mixture, and the like) is introduced into the heat exchanger where the coolant gas directly encounters and cools the semi-liquid fiber.
Typically, the heat exchanger comprises a passageway (e.g., generally of a cylindrical configuration) having end openings (e.g., a fiber inlet and a fiber outlet) for receiving and expelling the optical fiber, one or more coolant gas inlets for receiving the coolant gas, and one or more coolant gas outlets for discharging the coolant gas. The passageway generally extends from one end opening proximate a top of the heat exchanger to another end opening proximate a bottom of the heat exchanger. Thus, the passageway provides a corridor through which the optical fiber can pass. The coolant gas inlet (or inlets) can introduce coolant gas into the passageway while the coolant gas outlet (or outlets) can remove the coolant gas from the passageway. In a conventional system, a rate of flow of the coolant gas into the heat exchanger is manipulated and/or controlled with metering valves and flow meters.
If any of the spent coolant gas is recovered from the heat exchanger, typically proximate the outlet, the recovered coolant gas will typically be entrained with and/or carry impurities, debris, and the like (collectively “contaminants”). Typical contaminants include gases (e.g., nitrogen, oxygen, argon, and other gases present in the atmosphere), particulate substances (e.g., dust), and moisture. These contaminants can infiltrate the passageway, coolant gas inlet, and/or coolant gas outlet of the heat exchanger. The contaminants can collect and increase in concentration in the recovered coolant gas. The amount and/or concentration of contaminants in the recovered coolant gas can limit and/or restrict the amount of coolant gas that can be recycled and reused.
In order to reduce the amount and/or concentration of contaminants in the recovered coolant gas, a variety of solutions for decontaminating and/or purifying the coolant gas have been suggested. Coolant gas purification devices, systems, and/or methods are often employed. Such purification devices and/or methods are intended to remove some of the contaminants from the recovered coolant gas so that at least a portion of the recovered coolant gas can be recycled. However, the use of purification devices can represent a substantial expense in the optical fiber manufacturing process.
Unfortunately, without using a purification device, the amount of impurities contained within the recovered coolant gas can be substantial. As attempts are made to recycle more of the recovered coolant gas, the contaminant concentration within the recovered coolant gas can resultantly increase. Therefore, a diminishing amount of recovered coolant gas can be available for recycling.
Thus, an efficient and less complex apparatus and method for recovering and recycling coolant gas would be desirable.